A method for measuring the leaking current of a current transformer is disclosed. A standard voltage transformer, a mutual inductor check meter and a booster form a current transformer leaking current detection circuit. A rated voltage of a current transformer of a tested object is applied between the primary winding and secondary winding of the current transformer of the tested object, the K, D loops of the mutual inductor check meter are serially connected with the primary winding and the secondary winding, and the current I is measured. The primary side of the standard voltage transformer is parallelly connected with the high-voltage output terminal of the booster, and high voltage is isolated and reduced in accurate proportion. a, x loops of the mutual inductor check meter is parallelly connected with the secondary side of the standard voltage transformer to measure the voltage value U of the standard voltage transformer. The mutual inductor check meter calculates the conductance value G and susceptance value B between the primary winding and the secondary winding of the current transformer of the tested object, and the leakage current can be calculated according to the conductance value G, the susceptance value B, the secondary voltage value U of the standard voltage transformer and the rated voltage ratio K of the standard voltage transformer.